Twin Twin Transfusion Syndrome: Symptoms, Types, Causes and Treatment

Twin Twin Transfusion Syndrome (TTTS) is a rare but potentially life-threatening complication that can occur in identical twin pregnancies. Despite advances in prenatal care, TTTS remains a significant challenge for healthcare professionals and families alike. This article explores the symptoms, types, causes, and treatment options for TTTS, synthesizing the latest research to provide a comprehensive guide to this complex condition.

Symptoms of Twin Twin Transfusion Syndrome

TTTS can present with a range of symptoms, affecting both the mother and the developing twins. Recognizing these symptoms early is crucial for timely diagnosis and management.

Maternal	Fetal Donor	Fetal Recipient	Source
Rapid abdominal growth	Oligohydramnios (low amniotic fluid)	Polyhydramnios (high amniotic fluid)	1 4 5
Sudden weight gain	Small or absent bladder filling	Enlarged bladder, cardiomegaly	1 5 8
Tight or painful abdomen	Intrauterine growth restriction	Hydrops fetalis (fluid accumulation)	4 5 8
Shortness of breath	Anemia, pallor	Heart failure, hypertension	4 5 8

Table 1: Key Symptoms of TTTS

Maternal Symptoms

Mothers carrying monochorionic twins (identical twins sharing one placenta) may notice symptoms such as rapid abdominal growth, sudden weight gain, a tight or painful abdomen, and shortness of breath. These often result from the rapid accumulation of amniotic fluid (polyhydramnios), which can occur in TTTS. While these maternal symptoms are not specific to TTTS, they often prompt further investigation and ultrasound evaluation, leading to diagnosis 1 4.

Fetal Symptoms

TTTS affects each twin differently:

• Donor Twin: The donor twin loses blood to the recipient, leading to hypovolemia (low blood volume), oligohydramnios, small or absent bladder filling, intrauterine growth restriction, and sometimes anemia 1 5.
• Recipient Twin: The recipient twin receives excess blood, resulting in hypervolemia (high blood volume), polyhydramnios, an enlarged bladder, cardiomegaly (enlarged heart), hydrops fetalis (severe fluid accumulation), and risk of heart failure and hypertension 1 5 8.

Symptom Onset and Reporting

Symptoms often begin around 16–26 weeks of gestation, with a significant number of mothers reporting symptoms before diagnosis. However, research indicates that maternal complaints are sometimes dismissed, highlighting the importance of educating both healthcare providers and patients about the warning signs of TTTS 4.

Types of Twin Twin Transfusion Syndrome

TTTS is not a uniform condition; its severity and clinical presentation can vary widely. Understanding the types and staging of TTTS is key to appropriate management.

Type or Stage	Description	Clinical Significance	Source
Quintero Stage I	Polyhydramnios/oligohydramnios, normal Dopplers	Early, mild; may not progress	8 13 14
Quintero Stage II	Bladder of donor twin not visible	Moderate; risk increases	8 13
Quintero Stage III	Abnormal Dopplers (umbilical or venous)	Severe; higher risk of complications	8 13
Quintero Stage IV	Hydrops fetalis in either twin	Critical; urgent intervention	8 13
Quintero Stage V	Fetal demise in one or both twins	Most severe; poor prognosis	8 13

Table 2: TTTS Types and Stages (Quintero Classification)

The Quintero Staging System

The Quintero staging system is the most widely used framework for classifying TTTS severity:

• Stage I: There is a clear difference in amniotic fluid (polyhydramnios/oligohydramnios), but blood flow (Doppler) studies are normal.
• Stage II: The bladder of the donor twin is not visible on ultrasound.
• Stage III: Abnormal Doppler studies indicate compromised blood flow in either twin.
• Stage IV: There is evidence of hydrops fetalis (dangerous fluid buildup) in either twin.
• Stage V: One or both fetuses have died 8 13 14.

This staging guides clinicians in determining the urgency and type of intervention required.

Acute vs. Chronic TTTS

TTTS can present as either a chronic, progressive condition or as an acute event:

• Chronic TTTS develops gradually, often between 16–26 weeks, and can progress through the Quintero stages.
• Acute TTTS is rare, occurring suddenly (sometimes during labor or delivery), and may lead to rapid deterioration in fetal condition 17.

Other Classifications

Some researchers also differentiate TTTS based on placental vascular anatomy, such as the presence and type of vascular anastomoses (connections) between the twins’ circulations, which can influence both risk and severity 6 7.

Causes of Twin Twin Transfusion Syndrome

Understanding the root causes of TTTS is essential for prevention and targeted therapies. The condition arises from unique placental and vascular dynamics.

Cause	Mechanism or Factor	Impact on Twins	Source
Monochorionic placenta	Shared placental circulation	Risk of blood imbalance	1 5 6
Vascular anastomoses	Arteriovenous, artery-artery, vein-vein connections	Enable unbalanced transfusion	1 6 7
Unidirectional AV anastomoses	Blood flows from one twin (donor) to the other (recipient)	Leads to TTTS physiology	7 10
Renin-Angiotensin System (RAS)	Hormonal response to volemia changes	Exacerbates symptoms	5 11 7

Table 3: Main Causes and Mechanisms of TTTS

Monochorionic Placenta and Vascular Connections

TTTS only occurs in pregnancies where identical twins share a single placenta (monochorionic), which happens in about 10–20% of all twin pregnancies 1 5. Within the shared placenta, blood vessels from each twin can connect in various ways (anastomoses):

• Arteriovenous (AV) Anastomoses: Often unidirectional, these allow blood to flow from an artery of one twin to a vein of the other, creating the risk for chronic imbalance.
• Artery-Artery and Vein-Vein Anastomoses: Typically bidirectional; their presence can allow for compensatory blood flow and may protect against TTTS 7.

Placental mapping after birth often reveals multiple, complex vascular connections, but TTTS develops when there is an overabundance of unidirectional AV anastomoses without enough compensatory connections 6 7.

Pathophysiology: How Imbalance Occurs

• Donor Twin: Loses blood to the recipient through AV anastomoses, leading to hypovolemia, reduced kidney perfusion, decreased urine output (oligohydramnios), and growth restriction 1 5.
• Recipient Twin: Receives extra blood, leading to hypervolemia, increased urine output (polyhydramnios), high blood pressure, and risk of heart failure and hydrops 1 5 12.

Hormonal and Molecular Factors

The renin-angiotensin system (RAS), which regulates blood pressure and fluid balance, is upregulated in the donor twin due to low blood volume. Paradoxically, components of RAS can cross over to the recipient, contributing to hypertension and heart strain 5 11. This hormonal imbalance further drives the progression and severity of TTTS.

Why Only Some Twins Are Affected

Although most monochorionic twins have some vascular connections, only 10–15% develop TTTS. The exact reasons are not fully understood but likely relate to the number, type, and direction of placental vessel connections, as well as possible genetic or molecular predispositions 7 10.

Treatment of Twin Twin Transfusion Syndrome

TTTS is a medical emergency requiring specialized care. Treatment strategies depend on the stage of the disease, gestational age, and overall health of the mother and twins.

Treatment Option	Description	Effectiveness	Source
Fetoscopic Laser Surgery	Laser ablation of placental vessels	Most effective, improves survival, reduces neuro risks	1 9 13 14
Serial Amnioreduction	Draining excess amniotic fluid	Symptom relief; less effective long-term	13 14 16 17
Amniodrainage	Single or repeated fluid removal	Used in late gestation/acute cases	1 16 17
Expectant Management	Careful monitoring only	For mild/early cases	16

Table 4: Treatment Options for TTTS

Fetoscopic Laser Photocoagulation

Laser surgery is now the gold standard for moderate to severe TTTS (typically Quintero stages II–IV). This minimally invasive procedure involves:

• Inserting a small scope (fetoscope) into the uterus.
• Using a laser to seal off the abnormal blood vessel connections on the placental surface.
• Preventing further unbalanced blood flow between twins 1 9.

Research shows laser surgery results in higher survival rates, lower neurological impairment, and better long-term outcomes compared to serial amnioreduction 13 14. The "Solomon technique," which coagulates the entire vascular equator, further reduces recurrence and complications 9.

Serial Amnioreduction

This involves periodically removing excess amniotic fluid from the recipient twin's sac to relieve maternal symptoms and reduce preterm labor risk. While this can stabilize the pregnancy temporarily, it does not address the underlying vascular imbalance and is associated with higher rates of recurrence, mortality, and neurological complications compared to laser surgery 13 14 16.

Amniodrainage

Amniodrainage (single or repeated removal of amniotic fluid) is mainly used in acute or late-onset TTTS, especially after 26 weeks, or when laser surgery is not feasible. It can provide symptomatic relief and extend pregnancy but is less effective at improving long-term outcomes 1 17.

Expectant Management

Close monitoring without intervention may be considered in very mild or early-stage TTTS (Quintero stage I), especially if the condition does not progress. However, careful surveillance is critical as sudden deterioration can occur 16.

Long-Term Outlook and Follow-Up

Survivors of TTTS treated with laser surgery generally have good cardiovascular and neurological outcomes, though some risk of developmental delay and heart valve issues persists, particularly in recipient twins 5 12. Regular follow-up with pediatric specialists is recommended.

Conclusion

Twin Twin Transfusion Syndrome is a complex and serious complication unique to monochorionic twin pregnancies. Early recognition, accurate staging, and timely intervention can dramatically improve outcomes for both twins and families.

Key Takeaways:

• TTTS is caused by unbalanced blood flow between monochorionic twins due to abnormal placental vessel connections 1 5 6.
• Symptoms may include maternal discomfort, rapid abdominal growth, and distinct fetal signs such as oligohydramnios and polyhydramnios 1 4 5.
• The Quintero staging system helps guide management decisions, distinguishing between mild and severe disease 8 13 14.
• The gold standard treatment for moderate to severe TTTS is fetoscopic laser photocoagulation, which targets the root cause 1 9 13 14.
• Serial amnioreduction and amniodrainage provide temporary relief but are less effective at improving long-term outcomes 13 14 16 17.
• Early diagnosis and referral to specialized fetal medicine centers are vital for the best possible outcomes 1 8.

By understanding the symptoms, types, causes, and treatments for TTTS, families and clinicians can work together to navigate this high-risk condition with greater confidence and hope.